The present invention relates in general to electrophotographic devices such as photocopiers and the like, and more particularly to the magnet roll portion of a magnetic brush assembly for conveying powdery developer, commonly referred to as toner, used in magnetic brush developing, magnetic brush cleaning, etc.
A magnetic brush assembly includes a cylindrical nonmagnetic sleeve encasing a smaller diameter cylindrical magnet roll coaxially and rotatably mounted within the cylindrical sleeve. With the magnet roll held in position, the sleeve is rotated to convey magnetic particles of developer, the particles being temporarily held on the outer surface of the nonmagnetic sleeve due to the magnetic flux provided by a plurality of permanent magnet strips carried in parallel relation to each other on the cylindrical surface of the magnet roll within the sleeve.
In order to provide the required flux profile or gradient generated by the magnet strips circumferentially distributed about the cylindrical magnet roll, the magnet strips carried thereon must be straight and accurately positioned relative to the roll axis of rotation. Each magnet strip must be radially spaced from the roll axis by a fixed distance along its entire length. Also, each strip must be maintained in exact parallel relation with other strips and with the roll axis along its entire length. Such precise positioning requirements are difficult to obtain, especially when the magnet strips are constituted by flexible strips of extruded magnetic material, such as chlorinated polyethylene filled with barium ferrite particles, as is common in the art.
It is known in the art to provide a magnet roll having a one piece, cylinder-shaped, magnet carrier assembly with longitudinally extending channels circumferentially distributed about the carriers' axis of rotation. Flexible strips of extruded magnetic material are mounted and retained within the channels, the side walls or edges of the strips engaging the side walls of the channels.
In such a prior art structure, it is difficult and expensive to size and shape the channels and strips so as to precisely position the magnet strips as noted above. Other prior art magnet roll structures are set forth in U.S. Pat. Nos. 4,517,719, 4,558,294 and 4,587,699, all incorporated herein in their entirety by reference for purposes of background.